Virtual devices, such as virtual machines, are implemented in data centers where there are often many virtual devices or virtual machines running on the same server connecting to communication infrastructure, such as a communications infrastructure compliant with the Fiber Channel standard. Fiber Channel links may communicate data between the server and a Fiber Channel switch. Fiber Channel networks may slow down due to slow performance of one or more virtual devices or virtual machines.
In a Fiber Channel network, a recipient device issues credits which indicate to the transmitting device that it is allowed to send data packets. Each credit allows one packet (also called a frame) to be transmitted. The recipient device issues credits only when it can guarantee acceptance of a frame. When a frame arrives at the Fiber Channel switch egress port, the egress port checks if a credit is available, and only then is the packet transmitted. Once the recipient has received the frame, it is supposed to return a credit, in the form of a credit return, signaling that it is ready to receive another frame. Fiber Channel frames may be optical frames or “copper” frames depending on the media over which the Fiber Channel link is implemented.